The present invention relates to a current-voltage transformer for electronic house-service meters whose primary winding is magnetically coupled with a measuring coil via a ferromagnetic core and more particularly to such a transformer in which the measuring coil is inserted in an air gap of the transforming fastened and dimensional so that it lies within the cross sectional area of the core.
Electronic house-service meters having a current-voltage transformer require measuring value transducers for determining energy consumption. The transducers, transduce the consumer current into electrical quantities which can be further processed by electronic components. For this purpose it is required to convert consumer currents of, for example, 100 A into measuring currents or measuring voltages in the mA or mV range, respectively. Moreover, in the case of multi-phase current meters, the transformer must ensure a secure isolation. A further requirement is that the meter be insensitive to external magnetic interference fields and be independent of the conversion of a potential dc current premagnetization.
A current transformer configuration for avoiding the influence of external magnetic interference fields on the conversion results is known from DEP 36 19 423. In that configuration the primary conductor is implemented as a folded flat conductor with opposing conduction sections. There are two loop-form recesses which each form a current loop. To each current loop is assigned a measuring coil wound oppositely and provided with 50% of the total available windings. The two measuring coils are disposed between the two flat conductors conducting back and forth. The conductors comprise a magnetic shielding material. In this manner the measuring coils are largely shielded against magnetic interfering fields and the residual effect is compensated through the opposite winding of the two measuring coils.
The problem with this arrangement is that it is relatively expensive and space-consuming. Furthermore, due to the low coupling through the missing core of ferromagnetic material between primary winding and secondary coils, this arrangement supplies only low-level output signals.